Small Engines (Lawn Mowers, etc.): engine vibration valve gap ?, twin cylinder engines, clutch shoes

Question
I have a Tecumseh 6 hp HH65 hor. shaft go cart engine that starting vibrating super badly.  I took the torque converter loose and the vibration stopped.  
First I want to know the valve gap setting for the valves (I want to be sure this is right while I am at it. Do I just adjust the nut to do this?
Now I am wondering if the clutch is the problem.  It has a Comet 30 converter, the clutch springs look tight.  I next want to put the clutch back on the engine without putting the belt on it and try to see if the vibration is back.  If it is this may indicate a clutch problem.  If not then it may be in the driven assembly.  It has the nylon insert buttons (three)on it they look ok.  The vibration would occur before the cart gets going but on the rev up.  With out the converter the engine seemed to be OK.
Any info that might help me?
Thank you !!
Jimmy

Answer
Hello Jimmy:

From your Description it Sounds like the Clutch has Become Out of Balance. However, Here are the Instructions for Setting the Valves. **I Do Not Use the Setting Called for by the OEMs. I have Found that the Following Works Best. Remove the Valve Cover (on the Dead Cylinder for Twin Cylinder Engines). Set the Cylinder you are Setting the Valves on to Top Dead Center (Both Rocker Arms will have Play in them when the Engine is at TDC) on the Compression Stroke When Setting the Valve Clearance. Now Loosen the Valve Adjuster Locks and Set the Intake Valve Clearance to .004in -.006in and the Exhaust to .007in - .009in. I have had Better Performance Out of the Mowers and Less Burnt Valves Using these Settings. Be Sure the Piston is at TDC on the Compression Stroke.**  You have Stated the Engine Runs Good without the Clutch Assembly Attached to the Crankshaft. This Indicates the Clutch as the Problem for the Vibration. If 1 of the Clutch Shoes Wears More than the Other or a Section of the Shoe Breaks Off the Clutch will Cause the Vibration. If you Hit a Snag or this Does Not Correct the Problem,  I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Thanks.

Respectfully

John